The present invention relates to an illuminating device for rectangular surface, which device, has two identical lamps connected electrically in parallel, in particular for illuminating a liquid crystal cell from the rear.
Such illuminating devices are customary for indicating instruments in automotive vehicles and are therefore known.
The two lamps, provided for reasons of redundancy should be as identical as possible because of considerations of cost. Upon the failure of one lamp the illuminated surface should still be easily illuminated as uniformly as possible so that the indicating instrument can still be read well. In order to save energy, to be able to operate with lamps which are as weak as possible and to make the illuminating device as compact as possible, they must be arranged relatively close to the surface to be illuminated. In the previously known illuminating device, this necessarily leads to the result that upon failure of a lamp the illumination of the surface is relatively non-uniform.